GLAST Large Area Telescope Calorimeter Subsystem

1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope Calorimeter Subsystem 5.0 Crystal Detector Element Overview J. Eric Grove Naval Research Lab, Washington DC Calorimeter Instrument Scientist eric.grove@nrl.navy.mil (202)–767–3112

2. CDE Outline • Crystal Detector Element (Spec: LAT-DS-01133-02 ) • Design Drivers Eric Grove • Design Components Eric Grove • Responsibilities & Schedule Eric Grove • CsI(Tl) Crystals Leif Nilsson • CDE Manufacturing Didier BédérèdePhilippe Bourgeois

3. CDE Design Components • CDE has four components • CsI(Tl) crystal • Two PhotoDiode Assemblies (PDAs) • Hamamatsu S8576 Dual PhotoDiode (DPD) • Wire leads, soldered and staked • Wrapper • 3M Visual Mirror VM2000 film • Two end caps Optical Wrap PIN Diode (each end) Bond CsI Crystal End Cap Wireleads EM CDEs during wrappingand attachment of end caps

4. CDE Design Drivers

5. Since PDR … • Processes defined since PDR • Bonding of PDA to xtal • CTE mismatch between PDA and xtal causes stress in bond • Hard epoxies fail, silicones (without primer) don’t adhere • Need soft, flexible bond with strong adhesion • Solution: Silicone elastomer with primer. Bond laid up in mold that defines geometry. • Wrapping of xtal • Material is 3M VM2000 non-metallic, specular, reflective film • High light yield, good optical properties • Material is stiff, difficult to fold or wrap • Solution: Mold in mandrel at 120C for 2 hrs at final shape

6. CsI(Tl) crystals • CsI(Tl) gives high light yield with PDs and good stopping power for EM showers • LAT CAL numerology • 1536 crystals, each 326 mm x 26.7 mm x 19.9 mm • ~1200 kg of CsI • Need to characterize each crystal: 100% inspection and test • Dimensionally: completed CDE must fit in cell • Optically: xtal must have good light yield and taper • Procurement and testing are responsibility of GLAST Swedish Consortium • Institutions are Royal Institute of Technology (KTH), Stockholm University, and University of Kalmar • Responsibilities for crystal work: • Kalmar developed test benches and procedures • Kalmar and KTH test the crystals (mechanical / optical performance) • KTH tests boule samples (radiation harness test) • Performance spec: LAT-DS-00820-03

7. Photodiodes • Spectral response well matched to CsI(Tl) scintillation • Very small mass, volume, and power • Rugged • Made commercially in large quantities • Total 3072 required in LAT CAL • Reliable devices: only lot sample testing is required • Capacitance • Dark current • Photosensitivity • Procurement is joint responsibility of CEA/Saclay and NRL • Testing and processing is responsibility of CEA/Saclay • Lead for testing at CEA is Philippe Bourgeois • Spec: LAT-DS-00209-12 EM dual photodiode

8. Crystal Wrapper • Wrapper must be highly reflective • 3M VM2000 specular film • Gives 20-30% more light than standard diffusive white wraps (e.g. Tyvek, Tetratex) • Stable, rigid material will not wet xtal surface as Teflon-based wraps can (e.g. Tetratex) • Easy to form with hot molding (Swales) • Form VM2000 around aluminum mandrel in xtal form (with chamfers) • No loss in light yield or mechanical stability from hot molding • Procurement and molding are responsibility of CEA/Saclay • Molding/wrapping procedure: LAT-PS-00795-01

9. Responsibilities • Assembly flow for CDEs Amcrys CsI(Tl) Hamamatsu DPD 3M VM2000 Saclay: Assemble PDA Solder leadsStake leadsTest assy LLR: Machine end caps Saclay: Form wrapper Saclay: Assemble CDE Bond PDAs Wrap xtal Test assy Kalmar & KTH: Acceptance test

10. Schedule • Overview of schedule boundaries